Serena Williams of the US (L) embraces her sister and compatriot Venus Williams after defeating her in their quarterfinals match at the US Open Championships tennis tournament in New York, September 8, 2015. [Photo/Agencies]

The buzz around Arthur Ashe Stadium was like that of heavyweight title fight and the action on the court was much the same as Serena and Venus put family ties aside and slugged it out like sworn enemies.

"She's the toughest player I ever played in my life and the best person I know," said Serena in an on-court interview. "So it’s going against your best friend and at the same time going against the greatest competitor for me in women’s tennis, so it was really difficult today.

"When I'm playing her, I don't think of her as my sister, because she's playing so well, hitting big serves and running a lot of balls down."

The contest featured more intensity and emotion than in most of their other matches. Serena stared at the court and rarely looked up to make eye contact with her sister until the match was over and the sisters shared an embrace at the net.

The 33-year-old top seed, winner of 21 Grand Slam singles titles, took charge of the opening set by securing service breaks in the fifth and seventh games after a brilliant start by Venus.

However, Venus in the second set looked more like the player who has claimed seven Grand Slam singles titles, unleashing her power and drawing groundstroke errors from Serena for two service breaks that sent the match to a deciding third set.

Serena seized control early in the third and rode the momentum to the finish and a final four meeting with unseeded Italian Roberta Vinci.